1. Field of the Invention
The present invention relates generally to a method of detecting an erroneous signal. More particularly, the present invention relates to a method for detecting an erroneous direction of travel signal as used in a motor vehicle yaw control system.
2. Disclosure Information
Automotive vehicles with braking systems which respond to vehicle conditions as well as driver input have been produced. For example, when a particular yaw rate that is desired by a driver's steering wheel operation is not producing an adequate yaw rate, the braking system of the vehicle may compensate by altering a particular wheel's speed. However, when a vehicle is traveling reverse its normal operation direction, this response may not be appropriate. For this reason, it is necessary to provide the brake system with some indication of vehicle travel direction, e.g. forward or reverse. Further, it would be desirable to provide a system capable of robustly detecting an erroneous travel direction indication.
U.S. Pat. No. 5,686,662 ('662) addresses this problem by gathering two estimates of yaw rate, one estimate from the speeds of the left and right undriven wheels, and the other estimate from vehicle speed, steering wheel position, and lateral acceleration. A yaw rate is then measured using a yaw rate sensor. Finally a reverse travel condition is indicated if the signs of the first two estimates are opposite that of the measured yaw rate. However, under various operating conditions, the system described in '662 may have robustness difficulties. For instance, the correction coefficient, .omega..sub.c, is unknown at vehicle start-up, and thus for an indeterminate period of initial vehicle operation, one of the two estimates of vehicle yaw rate can not be independently determined in a manner which will allow robust detection of a reverse travel direction. Also, the '662 patent assumes that a difference in signs between the estimates and the measured yaw rate indicate a reverse travel direction, whereas such an instance could occur due to a yaw sensor fault.
It would be desirable to provide a method for indicating an erroneous travel direction that is robust to faults and disturbances of the wheel speed sensor, steering wheel sensor, and yaw rate sensor, operative from the moment of vehicle start-up.